Conventionally, a fuel cell separator has been known in which flow passages through which a gas, such as hydrogen or oxygen, or cooling water flows are formed by forming a plurality of protruding portions in a metal plate material. For example, methods disclosed by Patent Document 1 and Patent Document 2 have been proposed as methods for molding this fuel cell separator.
According to the molding method of Patent Document 1, as shown in FIG. 15(a), a small projection 421 is formed in a metal plate material 42 by means of a mold 411 and a mold 412 of a first molding tool 41. Thereafter, as shown in FIG. 15(b) and FIG. 15(c), the inside of the peripheral edge of the small projection 421 is pressed by a mold 431 and a mold 432 of a second molding tool 43, and a protruding portion 422 is formed.
According to the molding method of Patent Document 2, as shown in FIG. 16(a), a metal plate material 52 is pressed by a forward end surface of a convex part of a mold 511 of a first molding tool 51, and a small projection 521 is formed. Thereafter, as shown in FIG. 16(b), an oblique surface of a mold 512 and an oblique surface of the mold 511 of the first molding tool 51 are allowed to roll out (i.e., extend by applying pressure) sidewalls of the small projection 521 between both the oblique surfaces, and a protruding portion 522 is formed. Furthermore, as shown in FIG. 16(c), a forward end surface of a mold 531 and a bottom surface of a mold 532 of a second molding tool 53 that differs from the first molding tool 51 are allowed to roll out a top 524 of the protruding portion 522 between the forward end surface and the bottom surface. As a result, the top 524 of the protruding portion 522 becomes thinner, and the width of the top 524 becomes greater.
The following problems have resided in the conventional molding methods.
According to the molding method of Patent Document 1, both press working by use of the first molding tool 41 and press working by use of the second molding tool 43 are chiefly drawing-out molding. In detail, as shown in FIG. 15(a), the metal plate material 42 is pressed by a convex part 413 of the mold 412, and is drawn out. Thereafter, as shown in FIG. 15(b), the peripheral edge of the small projection 421 of the metal plate material 42 is pressed by a corner part 434 of the mold 432 and by a corner part 433 of the mold 431 in a narrow region. In this case, the position of the corner part 433 and that of the corner part 434 deviate in a height direction of the protruding portion of the metal plate material 42. Therefore, the metal plate material 42 is not only drawn out by both corner parts 433 and 434 but also bent on the corner parts 433 and 434 each of which serves as a fulcrum.
Thereafter, as shown in FIG. 15(c), the top of the small projection 421 of the metal plate material 42 is flattened by the mold 432 and the mold 431 between both the molds 431 and 432. On the other hand, pressing by means of the corner part 433 of the mold 431 is maintained in the narrow region.
As described above, the metal plate material 42 is drawn out by the mold 412, and is then drawn out by both the corner parts 433 and 434, and is drawn out by the corner part 433.
Therefore, the metal plate material 21 is drawn out, and reaches a state of being easily broken. Moreover, the metal plate material 21 is continuously pressed locally. Therefore, the stress distribution on the metal plate material 21 becomes non-uniform. In other words, the metal plate material 21 is continuously pressed near the corner part 433, and hence reaches a state of being easily broken.
According to the molding method of Patent Document 2, as shown in FIG. 16(a) and FIG. 16(b), the small projection 521 is formed by the mold 51, and then the sidewall 523 of the small projection 521 is rolled out by the first molding tool 51, and the protruding portion 522 is formed. In this case, as is apparent from FIG. 16(b), the sidewall 522 is formed by thinning only the protruding portion 523, and therefore the thickness of the sidewall 523 becomes insufficient. In this state, the strength distribution on the metal plate material 52 becomes non-uniform, and therefore the metal plate material 52 reaches a state of being easily broken. Additionally, according to the molding method of Patent Document 2, the protruding portion 522 is formed by the first molding tool 51, and then the top 524 of the protruding portion 522 is rolled out by the second molding tool 53, and the width of the top 524 becomes greater as shown in FIG. 16(c). In other words, the width of the top 524 is expanded by the movement of the material resulting from the roll-out of the top 524. The material that has moved in this way is gathered at the corner part of the top 524. Even in this state, the sidewall 523 remains thin, and is still in the state of being easily broken. Moreover, when the material gathers at the corner parts of both ends of the top 524, the stress distribution between the top 524 and the sidewall 523 greatly changes. Therefore, deformations, such as warpage or undulation, easily occur in the metal plate material 52 that has been molded.
As described above, according to the molding methods of Patent Documents 1 and 2, the fear of being broken or deformed is high, and therefore it is difficult to greatly extend the metal plate material 52 or to heighten the protruding portion 522. It is also conceivable that deformations are removed by leveling the stress distribution of the metal plate material 52. Therefore, there is a case in which annealing is applied after completing a molding operation. However, in this case, the processing step becomes complex.